In turning machines, a chuck body is usually mounted to a rotatable spindle, and the chuck body includes means for grasping a workpiece for rotation. The chuck and workpiece are then rotated in unison to perform a machining operation, and the workpiece is cut by a single point tool.
In bar feed turning machines, a length of raw bar stock extends from behind the head stock, through the headstock spindle and chuck, and out of the chuck face into the machining zone. The cutting tools machine a workpiece portion in the machining zone, and a cut-off tool then severs the workpiece portion to form a discrete, separated workpiece. Most often, the workpiece is thus considered finished and is removed from the machine at this point. Next, an increment of bar stock is fed out of the chuck face, the work is reclamped, and the machining operation is repeated. The bar stock may be fed by a stock pusher at the rear of the headstock, and it is usually necessary to provide an end stop in the machining zone, against which the stock can be pressed, in order to establish the proper length extending from the chuck face for machining. In a single spindle, two-axis turning machine, where a tool turret is supported on coordinately movable stacked X and Z slides, the X slide being movable radially of the workpiece and the Z slide being movable axially of the workpiece, the tool turret slides are used to end stop the bar stock. Generally, this function does not detract appreciably from the cycle time and the cutting tool can get back to work promptly after the stock length has been set. In machines having a main spindle and a subspindle, coaxially opposed to one another, for performing first and second operations on a workpiece (i.e., operations on both ends), the use of the tool slides for end stopping bar stock will substantially detract from the cycle time, since the tool turret should be sent to the subspindle area to perform the second operation, as the main spindle bar stock is fed outwardly.
In some instances, it is necessary to machine a second diameter on a workpiece, not concentric with a first machined diameter. The workpiece is usually taken to a second machine and then clamped in a rotary chuck or fixture which is adapted for supporting the primary axis off the axis of rotation, so that the part may be rotated about the axis of rotation and subsequently machined, producing the eccentric diameter.
The present invention obviates many of the difficulties inherent in the prior art, and has resulted in an improved method for turning a workpiece which permits a two-axis multi-spindle bar feed turning machine to produce a workpiece having eccentric diameters, in an efficient manner.